The development of photon-counting X-ray CT apparatuses is now being advanced. In a photon-counting X-ray CT apparatus, a sufficiently large count value of photons of X-rays is not obtainable due to the limitations of an X-ray detector. Consequently, there are cases in which the photon-counting X-ray CT apparatus receives the influence of statistical noise.
In the X-ray detector installed in the photon-counting X-ray CT apparatus, there are cases in which a photon is counted in an energy bin in which it should not be counted originally by escape. The escape is a phenomenon in which a photon that entered one of a plurality of X-ray detection elements of the X-ray detector gives to the entered X-ray detection element only a part of energy it has at the time of entering, is counted in an energy bin other than an energy bin including the energy it has at the time of entering, and escapes from the X-ray detector without interacting with other X-ray detection elements.
Furthermore, in the X-ray detector installed in the photon-counting X-ray CT apparatus, there are cases in which a photon is counted by an X-ray detection element by which it should not be counted originally by crosstalk. The crosstalk is a phenomenon in which a photon that entered one of a plurality of X-ray detection elements of the X-ray detector is scattered by the entered X-ray detection element, enters other X-ray detection elements, and is counted by the other X-ray detection elements.
Because of the phenomena described above, there have been cases in which the photon-counting X-ray CT apparatus is unable to obtain low-noise data.